Hallmarks of Aging Miniseries No. 2 Telomere Attrition

As cells divide, the telomere ends of chromosomes get shorter. Eventually, the enzyme that adds telomeric repeat sequences, telomerase, gets silenced and the telomeres are too short for cells to divide. Shortened telomeres are associated with aging cells that are senescent.

Telomeres at the ends of chromosomes, like all other sections of DNA, are prone to DNA damage, including double-strand breaks (DSBs). And unlike the rest of the chromosome, telomere DSBs aren’t fixed by the DNA repair pathway, as this would frequently lead to fused chromosomes and genomic instability. That’s why we have telomerase. However, telomerase expression is silenced in many adult cells, to curb rampant cell proliferation and tumorigenesis, and so telomeres get progressively shorter with age.